When you start doing in-house restorations it can be very stressful. What is the best way to achieve an aesthetic restoration? There are two main ways to process a restoration’s surface - either mechanical polishing, or staining and glazing. Both these techniques have their own pros and cons, and through this article you should have a better understanding of what may be best for your requirements.
Surface finishing may involve polishing or staining and glazing, and is the last step when processing your CAD/CAM restoration before cementation. It is this process that will give your restoration a high shine appearance which is desirable for aesthetic and hygienic reasons. A smooth restoration is essential. Bacteria don’t adhere to a smooth surface nearly as much as a rough surface, and it is also easier to clean for your patient. On top of that your restoration will have better colour stability long term as it doesn’t stain as much. After all, surface micro-roughness is why composite fillings and acrylic dentures change over time – these materials are quite porous and this surface porosity can only be polished to some extent. The surface finishing methods we will describe in this article are applicable to literally any dental ceramic material, as the core principles are identical across the entire industry.
Any dental material can be polished - metal, ceramic or acrylic etc. Therefore, it is arguably the method that is backed up by the longest and oldest clinical studies. As mentioned before, the core principles when polishing any material is mostly the same, whether or not you’re polishing e.max for your final restoration or a Telio CAD to temporize your prep.
Mechanical polishing requires sequential use of various polishers of different grit or coarseness, usually three levels – hard, medium and soft. The hardest, coarsest polisher is used to smooth the surface and remove any sprue remnants, as it removes the most material. Medium and soft polishers refine this further until the desired finish is achieved. For high-shine results, after polishing you need to buffer the restoration. This is done using diamond polishing paste (many dental companies sell this) with a bristle brush wheel or wool wheel. It’s crucial to use these polishers in the correct order as using a medium polisher after a softer one would just roughen the smoother surface.
Refer to our online courses on Milling, Processing and Finishing Restorations where we cover both, polishing and glazing, the tools and workflows, benefits and application.
Some clinicians may find polishing easier as it is not as technique demanding as staining and glazing. Keep in mind that it still requires patience because you need to ensure that every surface (with the exception of the intaglio) is polished meticulously. Typically the occlusal surface is trickier to polish. Fissures are notoriously difficult to reach with most polishers; flame-shaped polishers (or spiral wheels) are necessary. The pointy tip of these polishers blunts very quickly and you need to either replace them or keep sharpening them to a point using fine sandpaper, for example.
Polished multi-layered zirconia crown. In the occlusal close up you can see inadequately polished fissures that may get stained over time.
It is essential to use the correct polishers made for each individual material in order to polish successfully. Harder materials are not necessarily harder to polish. Although zirconia is notoriously difficult to polish in the mouth to a high standard, before cementation it can be quite an easy task if you use the correct tools.
It’s important to realize that when polishing you are removing some material from the surface of the restoration. Be careful when polishing the occlusal and interproximal contact areas and around the margin. Overzealous polishing of contact areas can result in open contacts for example. Softer materials like pre-crystallized silicate-based or resin-based ceramics, can easily become over-polished. Additionally, temporary PMMA materials can burn if too much pressure is applied, which complicates the polishing process itself and might even result in warpage.
The biggest issue with polishing is poor aesthetics when compared to good staining and glazing. CAD/CAM restorations are milled from monolithic blocks but natural crowns are not monolithic – there is a colour gradient, varying translucency, staining, enamel cracks etc. Multilayered CAD/CAM blocks are available nowadays and they might provide the colour gradient and even the translucency gradient, but that’s usually not enough to make a crown look natural. Mechanical polishing is therefore recommended for posterior teeth only.
Another method that will give your restorations a smooth, and shiny finish is glazing, usually accompanied with staining. Take note these terms are not interchangeable: glaze is a low fusing glass liquid/paste that is applied all over a restoration and results in a clear, shiny layer. Whereas stains are various pigments that are used for characterizing the otherwise monolithic restorations.
Various glazing and staining kits are available nowadays, for example IPS Ivocolor Starter Kit by Ivoclar or Universal Stain & Glaze Kit by Dentsply Sirona. These kits are basically compatible with multiple types of ceramics. We find that you can use any dental stain and glaze kit for any ceramic type, given that it is able to withstand the high firing temperatures. Therefore, resin-based hybrid ceramics (e.g. Cerasmart, Enamic, Tetric CAD etc.) are incapable of being processed in this way due to high resin content. They are vaporized if placed in a ceramic furnace and are therefore characterized with light-cured glaze and stains instead (e.g. Lite Art by Shofu or Optiglaze Colour).
It is the stains (or shades) that give a ceramic restoration its natural look. While layered restorations mirror natural tooth structures from within, stains imitate it on the surface. With the right training and practice it is possible to match a restoration to the rest of the dentition seamlessly. We regularly do this for our same-day e.max crowns and larger cosmetic cases, too.
E.max CAD stained and glazed in its pre-crystallized state (left) and the same crown after one firing cycle (right). Staining and glazing like this takes around 10 mins prior firing.
Compared to polishing, staining is a much more difficult to get right. When you first start, it is likely your first few restorations will look very ugly, as you will generally overdo it with stains or barely add anything at all. Keep at it! You just need to learn a few basics in order to achieve a nice, natural looking result. For example blue coloured stains can help you imitate enamel translucency which is something all dental ceramics struggle with. Dentine shades can help you match the restoration with the adjacent teeth, darken it a bit, but never lighten it. Don’t expect it to change the final shade completely, that comes from within the ceramic. It is still very important for the aesthetic success of the restoration to choose the right block shade as it is the core colour, its hue and value.
Check out our Comprehensive guide to characterizing monolithic restorations where we provide you with illustrated step-by-step tutorials on achieving natural looking restorations, both crown and bridges. We also cover surface texture enhancement!
Unlike polishing, glazing and staining doesn’t remove material at all - it adds some. This additional layer is usually so thin that with the right occlusal and interproximal contact relief values set in your CAD software, any adjustments prior cementing are rarely necessary. Keep in mind if you place a very thick layer of glaze on the interproximal contacts, not only will this look terrible, but will also inhibit proper seating of the restoration.
The biggest concern regarding glazing is that it can eventually wear off, which is most likely to occur on the occlusal aspect, while it tends to be longer lasting on the less functional surfaces. Ceramic underneath glaze layer is much rougher and these rough patches are then prone to staining and discolouration. You can always polish these spots without needing to remove the restoration as the worn glaze doesn't (realistically) compromise the restoration's function.
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Both methods - polishing or staining and glazing - have their place and use in material processing and dental ceramics. This is mostly dependent on personal preference – more technical oriented clinicians might have better results with polishing, while artistic hands will achieve incredibly aesthetic results with staining and glazing. In the case of anterior restorations, monolithic, polished-only surfaces are rarely ever indicated as natural teeth are not monolithic themselves – they vary in transparency, colour, staining, which is something even a multi-layered ceramic block cannot provide on its own. Therefore, for posterior restorations feel free to polish only, while for anterior restorations you will need to scratch up your staining and glazing skills.
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